An exemplary energy storage device includes a casing, a power generating element accommodated in the casing, a current collector conducted to at least one of positive and negative electrodes (also called positive and negative plates) in the power generating element, and an external terminal disposed on an outer surface of the casing and conducted to the current collector. As an example of energy storage device of this type, there has been known a nonaqueous electrolyte secondary battery (lithium ion secondary battery) disclosed in JP-A-2010-232187.
This battery has a plurality of power generating elements connected parallely to each other. More specifically, the power generating elements each have positive and negative plates and an insulating separator wound together with the plates. The wound objects (power generating elements) thus obtained each have a center axis and a radial direction perpendicular to the center axis. The power generating element has a flat cylindrical shape in cross section in the radial direction (hereinafter, also referred to simply as a flat cylindrical power generating element). Portions extracting the positive and negative electrodes from the power generating element (electrode extraction structure) have positive and negative current collecting connectors conductively connected correspondingly to the positive and negative electrodes of the power generating element, and positive and negative terminals (terminal bolts). These constituent elements are conductively connected with each other by way of a rivet and a terminal base made of metal.
In such an electrode extraction structure, the terminal base serves as a support member supporting the external terminal to keep constant strength, and also serves as a conductive member. More specifically, the terminal base and the current collecting connector are conductively connected with each other by way of a rivet. The rivet also serves as a portion fixing the terminal base and the current collecting connector to a lid.